Most known species have evolved during the “explosions” of diversity, shows the first analysis through “Tree of Life”

The British evolutionary biologist JBS Haldane would have quipped that all divine was obviously “an orderly affection for the beetles”. This “good engine” has transmitted an important truth: “the tree of life” – the family tree of all species, alive or extinct – is very unequal.

In places, it looks like a dense thicket of short twigs; Elsewhere, he only has sparse but long branches. Some groups tend to predominate: as Haldane pointed out, more than 40% of existing insects are beetles, while 60% of birds are gateways, and more than 85% of plants are flower plants.

But is such a concentration of species in some exceptionally large groups a universal phenomenon of life on earth? This question, important for our understanding of evolution and ecology, has long been the subject of controversy among biologists. But until recently, it was difficult to respond due to our poor knowledge of the number of existing species, their evolutionary relationships and the age of each group.

But now, scientists in the United States have finally provided an answer, published in Boundaries in ecology and evolution.

“Here, we show for the first time that most living species belong to a limited number of rapid radiation: that is to say that they form groups with many species that have evolved in a relatively short period,” said Dr. John J. Wiens, professor at the University of Arizona.

“More specifically, if we look among the kingdoms of life, among animal phyla and among plant phyla, we note in each case that more than 80% of the known species belong to the minority of groups with diversification rates of exceptionally high species.”

Wiens and his co -author, Dr. Daniel Moen, assistant professor at the University of California Riverside, have analyzed here the distribution of the wealth of species and diversification rates through clades – groups of species who have each evolved from a single ancestor, such as Phyla, Classes or Families.

Out on a limb

They did it for terrestrial plants, insects, vertebrates, for all animals and for all species of life. They analyzed the data on the richness of the species of each clade, the estimated age and diversification rate: that is to say the accumulation of new species over time.

They focused on 10 phyla, 140 orders and 678 families of land plants, jointly covering more than 300,000 species; 31 orders and 870 families of insects, including more than a million known species; 12 vertebrate classes, including more than 66,000 species; and 28 Phyla and 1,710 animal families with more than 1.5 million species. Finally, they analyzed 17 kingdoms and 2,545 families in life, including more than 2 million species.

The results were clear and consistent: whatever the hierarchical level or the group of organisms, the majority of existing species have proven to be limited to some disproportionately significant clades with diversification rates above the average.

It is believed that the “rapid radiations” of species occur when a new ecological niche opens: for example, when a herd of grassquit birds dispersed from Central America to the virgin territory of the Galápagos Islands about 2.5 million years ago to diversify in the famous Darwin Finches; Or when an evolutionary innovation like Powered flight caused the radiation of bats 50 million years ago.

See the forest for trees

“Our results imply that most of the diversity of life is explained by such relatively rapid radiation. We also suggest key features that could explain these rapid radiations, based on our results and results of previous studies,” said Wiens.

“These features include multicellularity in plants, animals and fungi through the kingdoms of life; land invasion and the adoption of a diet based on plants in arthropods in animal phyla; and the emergence of flowers and the pollination of insects in floral plants in vegetable phyla,” said Wiens.

However, a “known unknown” remains: the distribution of species within the kingdom of bacteria. About 10,000 species of bacteria are known to science, but current estimates for the real number vary from millions to billions of billions. However, the origin of bacteria dates back 3.5 billion years, and therefore the overall diversification rate between them is in fact quite low.

“If real bacterial wealth is much much higher than the richness described for other groups, then a clade with low diversification rates (namely bacteria) would contain the majority of species through life – this would be in contrast with our results. Consequently, we warn that our results apply mainly to the diversity of known species”, write the authors.